Limits...
Inefficient double-strand DNA break repair is associated with increased fasciation in Arabidopsis BRCA2 mutants.

Abe K, Osakabe K, Ishikawa Y, Tagiri A, Yamanouchi H, Takyuu T, Yoshioka T, Ito T, Kobayashi M, Shinozaki K, Ichikawa H, Toki S - J. Exp. Bot. (2009)

Bottom Line: An atbrca2a-1/atbrca2b-1 double mutant showed an additive increase in sensitivity to genotoxic stresses compared to each single mutant.In addition, it was found that atbrca2 mutant plants displayed fasciation and abnormal phyllotaxy phenotypes with low incidence, and that the ratio of plants exhibiting these phenotypes is increased by gamma-irradiation.Moreover, it was found that shoot apical meristems of the atbrca2a-1/atbrca2b-1 double mutant show altered cell cycle progression.

View Article: PubMed Central - PubMed

Affiliation: Division of Plant Sciences, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-8602, Japan.

ABSTRACT
BRCA2 is a breast tumour susceptibility factor with functions in maintaining genome stability through ensuring efficient double-strand DNA break (DSB) repair via homologous recombination. Although best known in vertebrates, fungi, and higher plants also possess BRCA2-like genes. To investigate the role of Arabidopsis BRCA2 genes in DNA repair in somatic cells, transposon insertion mutants of the AtBRCA2a and AtBRCA2b genes were identified and characterized. atbrca2a-1 and atbrca2b-1 mutant plants showed hypersensitivity to genotoxic stresses compared to wild-type plants. An atbrca2a-1/atbrca2b-1 double mutant showed an additive increase in sensitivity to genotoxic stresses compared to each single mutant. In addition, it was found that atbrca2 mutant plants displayed fasciation and abnormal phyllotaxy phenotypes with low incidence, and that the ratio of plants exhibiting these phenotypes is increased by gamma-irradiation. Interestingly, these phenotypes were also induced by gamma-irradiation in wild-type plants. Moreover, it was found that shoot apical meristems of the atbrca2a-1/atbrca2b-1 double mutant show altered cell cycle progression. These data suggest that inefficient DSB repair in the atbrca2a-1/atbrca2b-1 mutant leads to disorganization of the programmed cell cycle of apical meristems.

Show MeSH

Related in: MedlinePlus

γ-irradiation induces fasciation in wild-type (Nossen), atbrca2a-1 and atbrca2b-1 single mutants, and the atbrca2a-1/atbrca2b-1 double mutant.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC2692019&req=5

fig3: γ-irradiation induces fasciation in wild-type (Nossen), atbrca2a-1 and atbrca2b-1 single mutants, and the atbrca2a-1/atbrca2b-1 double mutant.

Mentions: The long-term effects of γ-irradiation on development in atbrca2 mutants transplanted in soil were investigated further. After high doses of γ-irradiation, although seedling growth of the wild type (Nossen), and atbrca2 single and double mutants was retarded (Fig, 1B, C), all these seedlings were able to survive and growth of these plants recovered (approximately 40–70% of control). One month after irradiation, shoot meristems underwent a transition from vegetative to inflorescence development, and the plants formed stems and floral meristems. It was found that γ-irradiation (600 Gy) accelerated the stem fasciation phenotype (including abnormal phyllotaxy) in atbrca2a-1 and atbrca2b-1 single mutants and in the double mutant plants (Nossen) (Fig. 3). Most interestingly, these phenotypes were also induced by γ-irradiation in wild-type plants (Nossen) (Fig. 3). Without γ-irradiation, the double mutant exhibited stem fasciation in 6.6% and 40% of plants transplanted to soil in the first and second experiments, respectively. Thus, the proportion of plants exhibiting stem fasciation differed markedly between the first and second experiments. Although every attempt was made to grow all the Arabidopsis plants in both experiments under identical conditions, even with sophisticated environmental control systems, subtle variations in conditions may occur. It is possible that such slight variations could have an effect on the ratio of plants that show stem fasciation. When imbibed seeds of the double mutant plants were irradiated with a 600 Gy dose of γ-rays, the frequency of stem fasciation increased by more than 20%. The frequency of stem fasciation was further increased by irradiation with a γ-ray dose of 700 Gy (data not shown). Thus, the proportion of plants showing stem fasciation increased with γ-irradiation in a dose-dependent manner. Each single mutant also showed stem fasciation at a low frequency without γ-irradiation, while γ-irradiation induced stem fasciation. Importantly, in wild-type plants, the frequency of stem fasciation was very low (<0.1%) under the growth conditions used, but these phenotypes were induced by γ-irradiation. In this study, the Nossen ecotype was used as a control plant since the mutant background is the Nossen ecotype. Imbibed seeds of several other ecotypes were also irradiated, and it was found that Nossen was one of ecotypes with relatively higher sensitivity to γ-irradiation. Ecotype Columbia was less sensitive to γ-irradiation than the other ecotypes (data not shown). These data suggest that the fasciation phenotypes in the atbrca2 single and double mutants could be linked to sensitivity to γ-irradiation.


Inefficient double-strand DNA break repair is associated with increased fasciation in Arabidopsis BRCA2 mutants.

Abe K, Osakabe K, Ishikawa Y, Tagiri A, Yamanouchi H, Takyuu T, Yoshioka T, Ito T, Kobayashi M, Shinozaki K, Ichikawa H, Toki S - J. Exp. Bot. (2009)

γ-irradiation induces fasciation in wild-type (Nossen), atbrca2a-1 and atbrca2b-1 single mutants, and the atbrca2a-1/atbrca2b-1 double mutant.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2692019&req=5

fig3: γ-irradiation induces fasciation in wild-type (Nossen), atbrca2a-1 and atbrca2b-1 single mutants, and the atbrca2a-1/atbrca2b-1 double mutant.
Mentions: The long-term effects of γ-irradiation on development in atbrca2 mutants transplanted in soil were investigated further. After high doses of γ-irradiation, although seedling growth of the wild type (Nossen), and atbrca2 single and double mutants was retarded (Fig, 1B, C), all these seedlings were able to survive and growth of these plants recovered (approximately 40–70% of control). One month after irradiation, shoot meristems underwent a transition from vegetative to inflorescence development, and the plants formed stems and floral meristems. It was found that γ-irradiation (600 Gy) accelerated the stem fasciation phenotype (including abnormal phyllotaxy) in atbrca2a-1 and atbrca2b-1 single mutants and in the double mutant plants (Nossen) (Fig. 3). Most interestingly, these phenotypes were also induced by γ-irradiation in wild-type plants (Nossen) (Fig. 3). Without γ-irradiation, the double mutant exhibited stem fasciation in 6.6% and 40% of plants transplanted to soil in the first and second experiments, respectively. Thus, the proportion of plants exhibiting stem fasciation differed markedly between the first and second experiments. Although every attempt was made to grow all the Arabidopsis plants in both experiments under identical conditions, even with sophisticated environmental control systems, subtle variations in conditions may occur. It is possible that such slight variations could have an effect on the ratio of plants that show stem fasciation. When imbibed seeds of the double mutant plants were irradiated with a 600 Gy dose of γ-rays, the frequency of stem fasciation increased by more than 20%. The frequency of stem fasciation was further increased by irradiation with a γ-ray dose of 700 Gy (data not shown). Thus, the proportion of plants showing stem fasciation increased with γ-irradiation in a dose-dependent manner. Each single mutant also showed stem fasciation at a low frequency without γ-irradiation, while γ-irradiation induced stem fasciation. Importantly, in wild-type plants, the frequency of stem fasciation was very low (<0.1%) under the growth conditions used, but these phenotypes were induced by γ-irradiation. In this study, the Nossen ecotype was used as a control plant since the mutant background is the Nossen ecotype. Imbibed seeds of several other ecotypes were also irradiated, and it was found that Nossen was one of ecotypes with relatively higher sensitivity to γ-irradiation. Ecotype Columbia was less sensitive to γ-irradiation than the other ecotypes (data not shown). These data suggest that the fasciation phenotypes in the atbrca2 single and double mutants could be linked to sensitivity to γ-irradiation.

Bottom Line: An atbrca2a-1/atbrca2b-1 double mutant showed an additive increase in sensitivity to genotoxic stresses compared to each single mutant.In addition, it was found that atbrca2 mutant plants displayed fasciation and abnormal phyllotaxy phenotypes with low incidence, and that the ratio of plants exhibiting these phenotypes is increased by gamma-irradiation.Moreover, it was found that shoot apical meristems of the atbrca2a-1/atbrca2b-1 double mutant show altered cell cycle progression.

View Article: PubMed Central - PubMed

Affiliation: Division of Plant Sciences, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-8602, Japan.

ABSTRACT
BRCA2 is a breast tumour susceptibility factor with functions in maintaining genome stability through ensuring efficient double-strand DNA break (DSB) repair via homologous recombination. Although best known in vertebrates, fungi, and higher plants also possess BRCA2-like genes. To investigate the role of Arabidopsis BRCA2 genes in DNA repair in somatic cells, transposon insertion mutants of the AtBRCA2a and AtBRCA2b genes were identified and characterized. atbrca2a-1 and atbrca2b-1 mutant plants showed hypersensitivity to genotoxic stresses compared to wild-type plants. An atbrca2a-1/atbrca2b-1 double mutant showed an additive increase in sensitivity to genotoxic stresses compared to each single mutant. In addition, it was found that atbrca2 mutant plants displayed fasciation and abnormal phyllotaxy phenotypes with low incidence, and that the ratio of plants exhibiting these phenotypes is increased by gamma-irradiation. Interestingly, these phenotypes were also induced by gamma-irradiation in wild-type plants. Moreover, it was found that shoot apical meristems of the atbrca2a-1/atbrca2b-1 double mutant show altered cell cycle progression. These data suggest that inefficient DSB repair in the atbrca2a-1/atbrca2b-1 mutant leads to disorganization of the programmed cell cycle of apical meristems.

Show MeSH
Related in: MedlinePlus